This application pertains to the art of motion conversion mechanisms, and more particularly, to such a mechanism for converting axial movement into rotational movement. The mechanism of the present application is particularly applicable for use in rotating exhaust valves on internal combustion engines and will be particularly described with reference thereto. However, it will be appreciated that the invention has broader aspects and may be used for imparting rotation to reciprocating elements other than internal combustion engine valves.
Valve rotators of a known type include first and second parts mounted for movement relative to one another axially and rotatably along and about a longitudinal axis. One part has grooves defining paths with inclined ramps on which rollable balls are positioned for imparting relative rotation to the parts in response to relative axial movement of such parts. In previous arrangements of this type, the grooves usually have axes lying on the circumference of a circle about the longitudinal axis. As a result, contact loads between the balls and their mating part are confined to a relatively narrow track on the mating part. This causes high contact loads between the balls and the mating part so that surface fatigue and wear occur relatively rapidly within this narrow track. Such high contact loads and rapid wear can be minimized by positioning a separate part with a formed raceway between the balls and the mating part but this makes the rotator more expensive and complicated.
Another suggested arrangement for minimizing high contact loads, and reducing surface fatigue and wear, is disclosed in U.S. Pat. No. 3,717,132 issued Feb. 20, 1973, to Van Slooten. In the Van Slooten arrangement, the grooves along which the balls move are positioned so that the balls move both circumferentially and radially relative to the longitudinal axis. The radial component of movement spreads surface fatigue and wear over a substantially larger area of the mating part so that life of the rotator is prolonged. However, the paths along which the balls move in the Van Slooten arrangement are located at the outer periphery of the one part and have a very short length. The very short path length is required in the Van Slooten arrangement in order that a circumferential spring will act against the balls in all positions of their movement along the paths. Such short paths limit the amount of relative rotation which can occur between the two parts due to rolling movement of the balls, and also limit the radial area over which surface fatigue and wear occurs on the mating part. The number of balls and grooves which can be provided within a given periphery is also limited when the grooves are located at the outer periphery of the one part so it is not possible to further reduce surface fatigue and wear by providing reduced contact pressures between the balls and the mating part.